Manufacture of organolead compounds



United States Patent 3 95 MANUFACTURE OF ORGANOLEAD COMPOUNDS Sidney M. Blitzer and Tillmon H. Pearson, Baton Rouge, La, assignors to Ethyl Corporation,- New York, N.Y., a corporation of Delaware No Drawing. Filed Jan. 7, 1957, Ser.- No. 632,634 4 Claims. (Cl. 260-437) This invention is concerned with a process for the preparation of organolead compounds, In particular it is directed to an improved process for the manufacture of tetraethyllead.

The present commercial process for the manufacture of tetraethyllead has been in use for a number of years and in general is satisfactory. However, it has certain disadvantages which are overcome by practicing the present invention. In particular, when reacting sodium-lead alloy with ethyl chloride only about 22 percent of the lead is converted to tetraethyllead. Thus, at least 75 percent of the lead originally employed is not alkylated. This lead mustbe recovered and reprocessed to sodiumlead alloy in order to make the process economical. Likewise valuable reaction space in the reaction vessel is occupied -by such unreacted lead which is a further disadvantage.-

Numerous improvements have recently been devised in the'abov'e process to consume the lead produced. Being satisfactory from the lead consumption stand-point they do however suil'er additional drawbacks in common with the commercial process in that they require an organo halide as the ethylating agent.

Hence, despite the attractiveness of the present commercial process and the improvements, it is still desired to obtain additional and improved techniques for the production of the valuable product, tet-raethyllead, and organolead products in general.

It is therefore an' object of this invention to provide a novel process for the manufacture of organolead compounds which overcomes the disadvantages of the present commercial process and those processes which have been proposed more recently as an improvement thereover. A particular object is to increase the conversion of lead to tetraethyllead above that obtained in the present commercial process without requiring the use of metallic sodium, metallic lead, or alkyl halogen compounds. I i l i i The above and other objects of this invention are accomplished by reacting a lead salt of a'complex inorganic acid containing a chalkogen with a stable non'lead organometallic compound. The organometallic compound is preferably one derived from the metals of groups IA, II and IIIA, particularly the organo'aluminum compounds.

In accordance with this invention, it has been discovered that it is unnecessary to start with a highly reactive lead alloy or to employ metallic lead at all to produce organolead compounds. The only lead compound required is a lead salt of a complex inorganic acid containing a chalkogen, namely oxygen or sulphur. By the term complex inorganic acid is intended those inorganic acids which contain oxygen or sulphur in the cation and additionally contain therein elements of the groups III, through VI of the periodic chart of the elements capable of forming complex ions with oxygen or sulphur.- The non-metallic elements of the groups IIIA, IVA, VA and VIA are particularly preferred. Such include boron, carbon, nitrogen, silicon, phosphorous, arsenic, selenium, and tellurium. Typical examples of such salts include the lead sulphates, sulphoriates, sulphinates, carbonates, nitrates, phosphates, both ortho and meta, pyrophosphates, persulphates, silicates, cyanates, thiocyauates, dithionate,

horates', both ortho and meta, selenate, the various arsenates and the like. Other lead salts which can be employed include, for example, those in which the cation comprises, in addition to the chalkogen, certain metals such as those of groups IIIB through VIB and IIIA through VA, for example, lead antimonate, tungstate, chromate, zirconate, molybdate, and the like. It is preferred however to employ the former lead salts, that is, those which do not contain the aforementioned metals, since they are more plentiful and produce better results. Of all the aforementioned lead salts, the lead sulphates are particularly desirable because of availability, more simplified processing, and more efficient conversion into organolead compounds.

In the organometallic compound, it is preferred that the metal or metalloid in question be attached only to carbon atoms in order to effect emcient utilization of this reactant. However, it is to be understood that the metal, in the case of polyvalent metals, in addition to having at least one metal to carbon bond can also be bonded to a halogen, e.g., chlorine, bromine, iodine and fluorine, or another metal, in particular the alkali or alkaline earth metals. The organo portion can be any organic radical including those having substituents in the radical such as a halogen provided such are essentially inert. In a preferred embodiment the organic radicals are hydrocarbon radicals, either acyclic or cyclic aliphatic radicals or aromatic radicals. Of the aliphatic radicals, it is preferred to employ the lower alkyl radicals having up to about 10 carbon atoms. Among the aromatic radicals which can he employed are included phenyl and hydrocarbon substituted phenyl radicals such as alkaryl radicals and fused-ring aromatic radicals such as naphthyl and hydrocarbon substituted fused-ring radicals. Of the aromatic radicals it is preferred to employ aromatic radicals containing up to about 10 carbon atoms. Thus, the organometallic compounds can be considered as organometallic alkylating or arylating agents with respect to the lead in the lead salt.

From a commercial standpoint the manufacture of tetraethyllead by this process is of the greatest importance. This embodiment can be illustrated by reference. to the following equation:

Illustrative of the alkylating or arylating agents which can be employed are methyl sodium, methyl lithium, dimethyl magnesium, methyl magnesium chloride, dimethyl zinc, trimethyl aluminum, tri-chloroethyl aluminum, sodium zinc tetramethyl, magnesium aluminum pentamethyl, ethyl sodium, diethyl magnesium, ethyl magnesium iodide, diethyl zinc, triethyl aluminum, methyl diethyl aluminum, sodium boro tetraethyl, ethyl aluminum sesq'uichloride, propyl lithium, propyl magnesium bromide, diisopropyl zinc, dipropyl cadmium, tripropyl aluminum, lithium aluminum tetrapropyl, octyl sodium, dioctyl magnesium, dioctyl zinc, sodium aluminum tetraoctyl, phenyl sodium, tricyclohexyl aluminum, sodium cyclopentadiene, sodium acetylide, phenyl lithium, diphenyl magnesium, diphenyl zinc, triphenyl aluminum, lithium aluminum tetraphenyl, tolyl sodium, tritolyl aluminum, lithium aluminum tetratolyl, naphthyl sodium, dinaphthyl magneisum, sodium aluminum tetranaphthyl, and the like. The organometallic compounds of the metals of group IIIA are particularly preferred.

In addition to the normal alkyl derivatives indicated heretofore, branched chain isomers can be employed. Likewise a mixture of two or more non-lead organometallic compounds can be employed, and if employed along with a redistribution catalyst there is produced a mixture of organolead compounds containing a multiplicit'y of organo radicals. Likewise, when the organo compound will not decompose.

radicals are dissimilar, mixed organolead compounds resu t.

According to this invention, as much as 50 percent of the lead is directly converted to organolead, or in a commercial embodiment to tetraethyllead. The unreacted lead portion is in a highly active form and particularly suitable for employment in the commercial process employing sodium-lead alloy. However, the lead can be employed in the present process by recycling after conversion to the appropriate lead salt. Thus by this process high yields of organolead product are obtained employing the economic lead salts such as the sulphates and nitrates which are readily available. Likewise the by-product salts formed have no destructive effect on the organolead product.

Our invention is adaptable to the production of organolead compounds generally, such as tetraethyllead, tetramethyllead, dimethyldiethyllead, tetracyclohexyllead, tetraphenyllead, triethylphenyllead and tetrapropyllead. Nevertheless, for convenience in the description hereafter, specific reference may be made to tetraethyllead, the most widely known because of its use as an antiknock agent. Whenever, this material is referred to, it is to be understood that other organolead compounds or mixtures containing lead to carbon bonds can be made by our process. While this invention is adapted to employ broadly the stable non-lead organometallic compounds defined heretofore, for convenience specific reference may be made hereinafter to employing aluminum triethyl which is the preferred embodiment in manufacturing the important antiknock material, tetraethyllead.

The process is generally conducted in the presence of an inert carrier liquid. Hydrocarbons of appropriate boiling point with respect to the organoleacl compound produced are satisfactory and can be chosen so as to provide a solution of the product suitable for other applications or so that they can be readily removed by distillation at a temperature at which the organolead Other inert carrier liquids are satisfactory and where the product is a liquid such as, for example, in the manufacture of tetraethyllead, the organolead compound itself can be employed. In such an operation, economy is effected by obviating the necessity of recovery by other means than merely filtration of the co-produced solids. Another class of carrier liquids comprises the liquid amines, the organic halides and ethers. The principal criteria of choice, therefore, of a carrier is the physical characteristic of the organolead compound produced, and the inertness of the liquid to the organoaluminum reactant. Certain of the aforementioned reactant carriers, while inert to the reactants, exhibit a beneficial effect on the reaction which may be considered catalytic in nature and contribute to the ease of reaction and rapidity of arriving at completion of the reaction at relatively lower temperatures and pressures. Of the aforementioned solvents the hydrocarbons particularly the aromatic hydrocarbons have been found most suitable since in these solvents higher yields are obtained. Typical examples of such solvents include the liquid aliphatic hydrocarbons such as the hexanes up to and including the octadecanes, the alkeues such as l-nonene, 2-octadecene, and the cycloaliphatics such as cyclopenteue, cylohexene, cyclohexane, cyclopentadiene and the like and the aromatic compounds as for example benzene, toluene, xylene, tetralin, and the like. It is to be understood that pure solvents need not be employed and mixtures thereof are equally suitable. For example, mixed hydrocarbons such as gasoline, diesel fuel, kerosene, and other petroleum fractions are satisfactory or mixtures of hydrocarbons and ethers, ethers and amines, amines and hydrocarbons, and the like.

The organometallic compounds employed as the reactants of this invention can be prepared by methods well known in the art. For example, the alkali metal compounds can be prepared by reaction of the alkali metal with an organomercury compound, The organoalkaline earth reactants can be produced by reacting the metal with an organic halide. Thus, diethyl magnesium is prepared by reacting ethyl chloride with magnesium turnings in the presence of diethyl ether, followed by addition of dioxane, thereby creating a separate liquid phase containing diethyl magnesium, halide-free, in a mixture of diethyl ether and dioxane. This procedure can be modified for the preparation of the organic metallic halides, for example, ethyl magnesium iodide, by ornitting the addition of the dioxane. A suspension of the desired compound in diethyl ether is obtained. Group IIIA organo compounds can be produced by the reaction of the group IIIA halide with an alkali metal organo compound. The group IIB reactants can be prepared by direct reaction of the metal and an organic halide. Thus, zinc diethyl is produced by reacting a zinc-copper couple with ethyl chloride and distilling diethyl zinc from the reaction mixture. The mixed metal organics are typified by lithium aluminum tetraethyl which can be prepared by reaction of lithium hydride and aluminum chloride to first form lithium aluminum hydride, which is then alkylated with ethylene. It is not intended, however, that the scope of this invention be limited to any particular method of producing the organometallic reactant.

The invention can be more fully understood from a consideration of the following examples.

Example I added. While maintaining a nitrogen atmosphere in the reactor, the reaction mixture was heated to the reflux temperature and maintained at this temperature for a period of 1 hour and 10 minutes. The mixture was then cooled to room temperature and filtered to remove solid constituents which are further purified and recovered for lead value. The filtrate was washed with an equal volume of water. The organolead product was transferred to a still for removal of the toluene by vacuum distillation and recovery of the tetraethyllead from the mixture. The yield of tetraethyllead was 54 percent.

Similarly when trimethyl aluminum, tripropyl aluminum, tricycloh'exyl aluminum, tr-iphenyl aluminum, tribenzyl aluminum, trioctyl aluminum and similar compounds in which boron, gallium or indium are substituted for aluminum are employed, satisfactory yields of the corresponding organolead products are obtained.

In general, the reaction of this process is completed in a relatively short period at elevated temperature but a somewhat longer time is required at lower temperatures. Usually a reaction time of between /2 to 20 hours is employed. Ordinarily however, the reaction will be completed within a period of about 4 hours. In the manufacture of tetraethyllead, employing especially aluminum triethyl and *lead sulphate, it is preferred to employ a reaction time of between /2 hour to 3 hours in order to minimize side effects.

The pressure employed in the reaction vessel is not critical. Usually the autogenous pressure created by the reaction, or the carrier liquid if employed, is used. Since the organolead compounds are relatively toxic it is desirable to employ a closed vessel in conducting the reaction and such may create elevated pressure when using low boiling reactants.

The temperature required to initiate the self-sustaining reaction of this invention varies with the organolead compounds being produced. In most instances reaction will commence at room temperature or lower. In general, with the lower molecular weight lead compounds such as tetraethyllead, it is preferred to employ temperatures in the range of 25 to 150 C. With higher molecular weight compounds, for example tetraphenyllead, it is preferred to operate in the range of 50 to 150 C. So far as now known, the reaction can be conducted satisfactorily at temperatures up to about the decomposition temperature of the organometallic reactant or the organolead product produced. Thermal stabilizers can be employed, however, to permit the operation of the reaction at still higher temperatures without the concomitant decomposition of the reactants or the organolead product. For example naphthalene, styrene and other well known stabilizers for organolead compounds, can be emploved in the reaction.

As the lead salt and in some instances the organometa'llic compound is a solid and generally a solvent therefore is not employed, it is preferred in order to provide a relatively rapid and controllable reaction to em ploy these reactants in finely divided form or at least in the form of small granules.

While in general a catalyst is not required for conducting this invention, certain materials do exhibit a catalytic effect on the reaction and in many instances their inclusion provides a smoother operation. Typical of such catalysts are heavy metal iodides, as well as iodine itself. organo halides, particularly the iodides, certain ketones such as acetone and methylethyl ketone, organometallic compounds and ethers and amines.

The proportions of the reactants are not critical and can be varied over a wide range. For example, the lead salts can be employed in excess or, conversely, the organometallic compounds in excess. It has been found however that the employment of the organometalli-c compound in excess is more desirable and effects a more complete conversion of the lead to the organolead product. In general, the proportions are such that the organometallic compound is employed in amount between about the stoichiometric amount and percent in excess.

The following examples serve to illustrate additional specific embodiments of the invention, however, it is not intended to be limited thereto.

Example II Employing the procedure of Example I when 14.6 parts of lead ortho phosphate were reacted with 4.2 parts of aluminum triethyl in 43 parts of dimethoxyethane under reflux conditions for 1 /2 hours, tetraethyllead was obtained in high yield.

In place of toluene or dimethoxyethane in the preceding examples as an inert carrier liquid, equally good results are obtained when other such diluents mentioned heretofore are employed. For example when other hydrocarbons such as cyclohexane, mixed hexanes, xylene, decene and the like, other others or amines such as dimethyl carbitol, dioxane, furan, diethyl amine, triethyl amine, organic halides such as methylene chloride, ethylene dichloride, or organometallics such as tetraethyllead itself are employed, similar results are obtained. Likewise, since one reactant is generally a liquid it is evident that the process can be constructed in the absence of a solvent. Additionally, mixtures of the aforementioned solvents can also be employed.

Example III When 17.9 parts of lead chromate were reacted with 4.2 parts of triethyl aluminum in 43 parts of dimethoxyethane at the reflux temperature for 1 /2 hours, tetraethyllead was obtained in high yield.

Example IV To 18.1 parts of lead thiocyanate was added 4.2 parts of aluminum triethyl While suspended in 65 parts of toluene at the reflux temperature for a period of 3 hours. The yield of tetraethyllead was 39 percent.

7 Example V Employing the procedure essentially as described in Example I, 20.1 parts of lead nitrate were: reacted 4.2 parts of aluminum triethyl at room temperature for 1 hour while the reactants were suspended in 43 parts of dimethoxyethane. The yield of tetraethyllead was 50.3 percent.

The following examples will demonstrate the employment of other organometallic compounds according to this invention.

Example VI When ethyl sodium is reacted with lead sulphate while suspended in the dimethyl ether of diethylene glycol, essentially as described in Example I, an essentially quantitative conversion to tetraethyllead is obtained.

In place of ethyl sodium in the preceding example, phenyl sodium, benzyl sodium, ethyl lithium, amyl potassium and the like organometallic compounds can be employed to produce similar results.

Example VII When sodium aluminum tetraethyl is reacted with lead sulphate employing toluene as the diluent at the reflux temperature for 2 hours, tetraethyllead is obtained in high yield.

Example VIII In this run 10 parts of ethyl aluminum sequichloride are reacted with 18 parts of lead nitrate in cyclohexene at the reflux temperature for 3 hours. An essentially quan titative conversion of the lead to tetraethyllead is obtained.

In place of ethyl aluminum sequichloride in the above example, when ethyl magnesium bromide, ethyl calcium iodide, ethyl zinc chloride, or diphenyl aluminum chloride are substituted, the corresponding organolead compounds are obtained in high yield.

Example IX Dicyclohexyl magnesium is prepared by reacting cyclohexyl chloride with magnesium turnings in the presence of diethyl ether. At the completion of the reaction dioxane is added to the reaction mixture creating a separate reaction phase containing dicyclohexyl magnesium, halide free. This phase is separated and then reacted With 15.0 parts of lead sulphate at the reflux temperature for 3 hours. An essentially quantitative conversion of the lead to tetracyclohexyllead is obtained.

Example X When diethyl zinc is reacted with lead sulphate employing triethyl amine as the liquid diluent at the reflux temperature for 3 hours, tetraethyllead is obtained in high yield.

A particularly advantageous and preferred method of utilizing the process of this invention as specifically directed to a commercial method for manufacturing tetraethyllead comprises starting with free aluminum and hydrogenating to produce the corresponding aluminum hydride or preparing ethyl aluminum hydride by employing triethyl aluminum as a catalyst in the aluminum hydrogenation reaction. A second step then comprises reacting the aluminum hydride or ethyl aluminum hydride produced with ethylene to produce triethyl aluminum which is then reacted with the lead salt in accordance with the foregoing description of the present invention.

Having thus described the present invention it is not intended that it be limited except as set forth in the following claims.

We claim:

1. A process for the manufacture of an organolead compound which comprises reacting an organometallic compound wherein the metal is selected from the group consisting of group I-A, II, and III-A metals of the periodic chart of the elements and wherein the organo groups are selected from the group consisting of alkyl and aryl 7 8 radicals with lead sulfate in the presence of an essentially at a temperature between about 25 to 150 C. in the inert organic diluent. presence of an essentially inert organic diluent. 2. A process for manufacturing an alkyllead compound 4. The process of claim 3 wherein said inert organic which comprises reacting lead sulphate in the presence diluent is toluene. of an essentially inert organic diluent with an alkyl metal- 5 he compound wherein the metalllc element is selected eferences cued m the file of this patent from the group consisting of metals of groups IA, II, UNITED STATES PATENTS and III-A. 1,798,593 Daudt Mar. 31, 1931 3. A process for manufacturing tetraethyllead which 1,938,180 Groll Dec. 5, 1933 comprises reacting lead sulphate with triethyl aluminum 10 1,949,948 Alleman Mar. 6, 1934 

1. A PROCESS FOR THE MANUFACTURE OF AN ORGANOLEAD COMPOUND WHICH COMPRISES REACTING AN ORGANOMETALLIC COMPOUND WHEREIN THE METAL IS SELECTED FROM THE GROUP CONSISTING OF GROUP I-A, II, AND III-A METALS OF THE PERIODIC CHART OF THE ELEMENTS AND WHEREIN THE ORGANO GROUPS ARE SELECTED FROM THE GROUP CONSISTING OF ALKYL AND ARYL RADICALS WITH LEAD SULFATE IN THE PRESENCE OF AN ESSENTIALLY INERT ORGANIC DILUENT. 